The arrival of South Sudan's rebel leader Riek Machar in the capital Juba has been postponed for the second time due to logistical problems, a rebel spokesman has said. Machar was due to arrive in the capital on 18 April to resume his position of vice-president.

It is believed that the new delay has been caused by the South Sudanese government's request that a plane carrying Machar's chief of staff General Simon Gatwech must obtain clearance to fly into South Sudan airspace. The reason might be motivated by the fact that Gatwech allegedly requested extra soldiers and an arsenal, including missiles and tanks, for his arrival in Juba, the BBC reported.

Machar, who left Juba when the conflict erupted in 2013, will work with President Salva Kiir to form a unity government. His reinstatement is part of a series of measures contained in a peace deal aimed at ending a civil war that has caused the deaths of thousands.

South Sudan descended into civil war in 2013 when Kiir, from the Dinka ethnic group, fired Machar, from the Nuer group, and his cabinet. The dismissal followed Kiir's decision to replace members of the army and government amid rumours of a coup plot by Machar.

August 2015 peace deal: the key elements

Both parties commit to immediate cessation of violence

Machar to be reinstated as vice-president

Foreign troops to pull out

Military personnel in Juba to be replaced by police and guards

Creation of transitional government that will stay in power for 30 months

Presidential elections to be held 30 days before end of transitional government mandate

Ethnic-related violence then spread, with militia groups carrying out attacks in villages and areas known to be inhabited by either Dinka or Nuer tribes.

More than 10,000 civilians have so far been killed in the conflict, amid allegations of crimes against humanity committed by both sides, including extra-judicial killings, abductions, rape, torture and use of child soldiers. At least two million people have also been displaced.

Although the two warring factions have signed at least seven peace deals, the violence has continued, and a January report from the African Union blamed both opposing leaders for the ongoing unrest.